Most of the existing leading-edge light bulb dimming circuitries use triad to control the phase of supply voltage, which always produces large surge current spikes and thus has a poor applicability in capacitive impedance LED lamps, electronic spotlights, electronic ballast controlled fluorescent lamps, electronic energy-saving lamps, etc.
Most of the existing trailing-edge light bulb dimmers use two input wires and two output wires (e.g., four-wire systems), which makes the installation more complicated due to additional wires needing to be connected. For example, a main power supply 7 such as an indoor electrical junction box generally provides one live wire and one neutral wire for connecting to lighting loads; therefore, if a three-wire or four-wire system is to be installed, additional wires need to be provided, and the original electrical wiring will need to be changed, which results in increased labor and material costs.
Chinese Patent Application No. 00125744.7 discloses a trailing-edge phase-controlled four-wire system light bulb dimmer. Chinese Patent Application No. 201120003889.0 discloses a two-wire system trailing edge dimmer, in which the triggering circuit and the power supply circuit are connected together. The dimming adjustment not only changes the output voltage, it also changes the voltage level of the supply voltage. Therefore, there is a requirement for further improvement.